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研究者情報

マスター

アカウント（マスター）

  • 氏名

    水田　浩之(ミズタ　ヒロユキ), ミズタ　ヒロユキ

所属（マスター）

  • 水産科学研究院　海洋応用生命科学部門　育種生物学分野

所属（マスター）

  • 水産科学研究院　海洋応用生命科学部門　育種生物学分野

独自項目

syllabus

  • 2021, 育種生物学特論Ⅰ, Advanced Aquaculture Genetics and Genomics Ⅰ, 修士課程, 水産科学院, polyploid, triploid, tetraploid, meiosis, teleost, unreduced gametogenesis, germ cells
  • 2021, 育種生物学特論Ⅱ, Advanced Aquaculture Genetics and Genomics Ⅱ, 修士課程, 水産科学院
  • 2021, Introduction to Fisheries Sciences Ⅱ（水産科学汎論Ⅱ）, Introduction to Fisheries Sciences Ⅱ, 修士課程, 水産科学院, 水産科学，海洋生物学，生物多様性，生物資源, 環境, 資源探査, 漁業技術, 持続可能性, 環境保全, 養殖, 遺伝学, 生命工学, 微生物学, 化学，食糧科学,生物安全性
  • 2021, 大学院共通授業科目（一般科目）：自然科学・応用科学, Inter-Graduate School Classes(General Subject):Natural and Applied Sciences, 修士課程, 大学院共通科目, polyploid, triploid, tetraploid, meiosis, teleost, unreduced gametogenesis, germ cells
  • 2021, 水圏生物学, Aquatic Biology, 学士課程, 水産学部, 学名、命名法、系統樹、分類体系、学術標本、種多様性
  • 2021, 水産科学英語Ⅰ, English for Fisheries Sciences I, 学士課程, 水産学部, 水産生命科学英語、水産技術英語
  • 2021, 環境と人間, Environment and People, 学士課程, 全学教育, 海、河川、生命、細胞、遺伝子、魚、海藻、微生物、代謝、進化
  • 2021, 水産増殖学, General Aquaculture, 学士課程, 水産学部, 水産増殖，水産養殖，種苗生産，染色体地図，遺伝的多様性，遺伝マーカー，育種，遺伝的管理，魚病，海藻
  • 2021, 海洋植物学, Marine Botany, 学士課程, 水産学部, 海洋植物・多様性・生活史・発生・成長・生殖・環境応答・育種・藻場・生物機能・分子生物
  • 2021, 基礎生命科学実験, Basic Laboratory Works on Life Science, 学士課程, 水産学部, 組織　器官　解剖　切片　基本操作　緩衝液　吸光度分析
  • 2021, 発生・組織学, Embryology and Histology, 学士課程, 水産学部, 器官、組織、細胞、生殖、発生

researchmap

プロフィール情報

学位

  • 博士（水産学）（北海道大学）

プロフィール情報

  • 姓

    水田

  • 名

    浩之

  • ID各種

    201301026266335601

業績リスト

研究キーワード

  • 生活環制御   防御応答   栄養塩   コンブ類   成熟   子嚢斑   培養   環境要因   植物成長調整物質   再分化   植物生長調整物質   抵抗性   組織培養   種苗   光質   活性酸素   マコンブ   ヨウ素   増殖   繁殖   生態系モデル   基礎生産   スサビノリ   

研究分野

  • ライフサイエンス / 水圏生産科学 / 海藻増養殖
  • ライフサイエンス / 水圏生命科学 / 海藻繁殖生理学

経歴

  • 2013年 - 現在 北海道大学 水産科学研究研究院 教授

論文

  • Toshiki Uji, Takuya Kandori, Hiroyuki Mizuta
    Frontiers in Plant Science 15 2024年08月06日 [査読有り]
     
    Saccharina japonica, a significant brown macroalga in the Pacific Ocean, serves as a food source and industrial material. In aquaculture, collecting mature sporophytes for seedling production is essential but challenging due to environmental changes. In this study, transcriptomic analysis of vegetative and sorus tissues was done to identify differentially expressed genes (DEGs) and enhance our understanding of sorus formation regulation in S. japonica. KEGG pathway and Gene Otology (GO) analysis revealed that upregulated DEGs were involved in folate biosynthesis, riboflavin metabolism, and amino acid biosynthesis. In addition, the upregulation of genes associated with cell wall remodeling, such as mannuronan C-5-epimerases, vanadium-dependent haloperoxidases, and NADPH oxidase, was observed in sorus parts. Meanwhile, downregulated DEGs in sorus portions included genes related to chloroplast function. These findings will help us understand the regulatory mechanisms behind sorus formation in S. japonica and extracellular matrix remodeling in brown algae.
  • Shoichi Akaike, Hiroyuki Mizuta
    European Journal of Phycology 59 2 218 - 231 2024年02月27日 [査読有り]
  • Kenshiro ABE, Inori ARIGA, Toshiki UJI, Hiroyuki MIZUTA
    Cahiers de Biologie Marine 65 73 - 85 2024年01月 [査読有り]
  • Shinnosuke Ueda, Hiroyuki Mizuta, Toshiki Uji
    MOLECULAR BIOTECHNOLOGY 2022年09月 [査読有り]
     
    Epigenetic regulation by histone modification can activate or repress transcription through changes in chromatin dynamics and regulates development and the response to environmental signals in both animals and plants. Chromatin immunoprecipitation (ChIP) is an indispensable tool to identify histones with specific post-translational modifications. The lack of a ChIP technique for macroalgae has hindered understanding of the role of histone modification in the expression of genes in this organism. In this study, a ChIP method with several modifications, based on existing protocols for plant cells, has been developed for the red macroalga, Neopyropia yezoensis, that consists of a heterogeneous alternation of macroscopic leaf-like gametophytes and microscopic filamentous sporophytes. ChIP method coupled with qPCR enables the identification of a histone mark in generation-specific genes from N. yezoensis. The results indicate that acetylation of histone H3 at lysine 9 in the 5 ' flanking and coding regions from generation-specific genes was maintained at relatively high levels, even in generation-repressed gene expression. The use of this ChIP method will contribute significantly to identify the epigenetic regulatory mechanisms through histone modifications that control a variety of biological processes in red macroalgae.
  • Toshiki Uji, Hiroyuki Mizuta
    JOURNAL OF APPLIED PHYCOLOGY 34 3 1527 - 1536 2022年06月 [査読有り]
     
    Heat stress disrupts algal growth, development, and physiological processes, such as photosynthesis, and eventually decreases seaweed productivity. Previous studies of crop plants have revealed that exogenous application of phytohormones prior or parallel to stress can alleviate the negative effects of abiotic stressors, including heat stress. However, there is limited information on phytohormone-induced tolerance to abiotic stressors in seaweed. In the present study, the application of the major plant hormones abscisic acid and salicylic acid failed to mitigate the negative effects of heat stress on the marine red alga Neopyropia yezoensis, whereas 1-aminocyclopropane-1-carboxylic acid (ACC), the direct precursor of the plant hormone ethylene, regulates thermotolerance. In addition, the ACC analogs 1-aminocyclobutane-1-carboxylic acid and alpha-aminoisobutyric acid enhanced tolerance to heat stress. ACC increased the expression of genes involved in antioxidant defense systems to protect photosynthesis and respiration. These results suggest ACC acts as a phytohormone to mitigate the impact on heat stress independent of ethylene in N. yezoensis.
  • Sayaka Kominami, Hiroyuki Mizuta, Toshiki Uji
    MARINE BIOTECHNOLOGY 24 2 393 - 407 2022年04月 [査読有り]
     
    Many organisms are subjected to a daily cycle of light and darkness, which significantly influences metabolic and physiological processes. In the present study, Neopyropia yezoensis, one of the major cultivated seaweeds used in "nori," was harvested in the morning and evening during light/dark treatments to investigate daily changes in gene expression using RNA-sequencing. A high abundance of transcripts in the morning includes the genes associated with carbon-nitrogen assimilations, polyunsaturated fatty acid, and starch synthesis. In contrast, the upregulation of a subset of the genes associated with the pentose phosphate pathway, cell cycle, and DNA replication at evening is necessary for the tight control of light-sensitive processes, such as DNA replication. Additionally, a high abundance of transcripts at dusk encoding asparaginase and glutamate dehydrogenase imply that regulation of asparagine catabolism and tricarboxylic acid cycle possibly contributes to supply nitrogen and carbon, respectively, for growth during the dark. In addition, genes encoding cryptochrome/photolyase family and histone modification proteins were identified as potential key players for regulating diurnal rhythmic genes.
  • Toshiki Uji, Takuya Kandori, Shiho Konishi, Hiroyuki Mizuta
    BMC PLANT BIOLOGY 22 1 2022年04月 [査読有り]
     
    Background 1-aminocyclopropane 1-carboxylic acid (ACC) is the immediate precursor of the plant hormone ethylene. However, recent studies have suggested that ACC also acts as a signaling molecule to regulate development and growth independently from ethylene biosynthesis. In red algae, ACC stimulates the switch from a vegetative to a sexual reproductive phase. However, despite evidence that ACC signaling in plants and algae is widespread, the mechanistic basis of the ACC signaling pathway remains unknown. Results We demonstrate that exogenous ACC increased the activity of phospholipase D (PLD) and induced the accumulation of PLD transcripts in the marine red alga Neopyropia yezoensis. The product of PLD, the lipid second messenger phosphatidic acid (PA), also increased in response to ACC. Furthermore, the pharmacological inhibition of PLD by 1-butanol blocked ACC-induced spermatangia and carpospore production, but the inactive isomer t-butanol did not. In addition, 1-butanol prevented ACC-induced growth inhibition and inhibited transcript accumulation of genes upregulated by ACC, including extracellular matrix (ECM)-related genes, and alleviated the transcriptional decrease of genes downregulated by ACC, including photosynthesis-related genes. Conclusions These results indicate that PLD is a positive regulator of sexual cell differentiation and a negative regulator of growth. This study demonstrates that PLD and its product, PA, are components of ACC signaling during sexual reproduction in N. yezoensis.
  • Toshiki Uji, Shinnosuke Ueda, Hiroyuki Mizuta
    Phycology 2 1 45 - 59 MDPI AG 2022年01月06日 [査読有り]
     
    Extracellular matrix (ECM) proteins play crucial roles in the regulation of cell proliferation and differentiation. We identified homologous genes encoding ECM proteins that are known to associate with integrins in animal cells in red macroalga Neopyropia yezoensis. Four genes encoding spondin domain-containing proteins (NySPLs) and eight genes encoding fasciclin domain-containing proteins (NyFALs) from N. yezoensis were selected for bioinformatics and expression analysis in order to obtain insights into the roles of ECM proteins for the life cycle. NySPLs had eight β-strands with two contiguous α-helices, which were similar to those of the F-spondin domain of animals. NyFALs had conserved H1 and H2 motifs and a YH motif between the H1 and H2 regions. Quantitative reverse transcription polymerase chain reaction showed that NySPL1–3 and NyFAL8 transcripts were highly accumulated in mature gametophytes that formed the spermatia. Furthermore, expressions of all NySPLs were upregulated in response to the ethylene precursor 1-aminocylopropane-1-carboxylic acid that induces gametogenesis. NyFAL1, 4 were highly expressed in sporophytes, whereas NyFAL2, 3, 5, 6, and 7 were overexpressed in gametophytes, especially at the vegetative stage. These findings facilitate future research on ECM architecture in the unique life cycles of red macroalgae.
  • Toshiki Uji, Hiroyuki Mizuta
    Frontiers in plant science 13 1019334 - 1019334 2022年 [査読有り]
     
    Seaweeds or macroalgae are important primary producers that serve as a habitat for functioning ecosystems. A sustainable production of macroalgae has been maintained by a diverse range of life cycles. Reproduction is the most dynamic change to occur during its life cycle, and it is a key developmental event to ensure the species' survival. There is gradually accumulating evidence that plant hormones, such as abscisic acid and auxin, have a role on the sporogenesis of brown alga (Saccharina japonica). Recent studies reported that 1-aminocylopropane-1-carboxylic acid, an ethylene precursor, regulates sexual reproduction in red alga (Neopyropia yezoensis) independently from ethylene. In addition, these macroalgae have an enhanced tolerance against abiotic and biotic stresses during reproduction to protect their gametes and spores. Herein, we reviewed the current understanding on the regulatory mechanisms of red and brown algae on their transition from vegetative to reproductive phase.
  • Toshiki Uji, Hiroyuki Mizuta
    AQUACULTURE RESEARCH 52 12 6814 - 6817 2021年08月 [査読有り]
  • Extracellular silicate uptake and deposition induced by oxidative burst in Saccharina japonica sporophytes (Phaeophyceae)
    Hiroyuki Mizuta, Toshiki Uji, Hajime Yasui
    Algal Research 58 102369  2021年06月07日 [査読有り][通常論文]
  • α-aminoisobutyric acid mimics the effect of 1-aminocyclopropane-1-carboxylic acid to promote sexual reproduction in the marine red alga Pyropia yezoensis (Rhodophyta)
    Harune Endo, Hiroyuki Mizuta, Toshiki Uji
    Jounarl of applied phycology 33 1081 - 1087 2021年01月02日 [査読有り][通常論文]
  • Sexual Reproduction via a 1-Aminocyclopropane-1-Carboxylic Acid-Dependent Pathway Through Redox Modulation in the Marine Red Alga Pyropia yezoensis (Rhodophyta)
    Toshiki Uji, Harune Endo, Hiroyuki Mizuta
    Frontiers in plant science 11 60  2020年02月12日 [査読有り]
  • Ryo Yanagisawa, Naoki Sekine, Hiroyuki Mizuta, Toshiki Uji
    JOURNAL OF APPLIED PHYCOLOGY 31 5 3317 - 3329 2019年10月 [査読有り][通常論文]
     
    The marine red algal genus Pyropia, class Bangiophyceae, includes dioecious and monoecious species; however, the molecular mechanisms underlying control of their sexual reproduction are still poorly understood. In the present study, we demonstrated that application of the ethylene precursor, 1-aminocyclopropane-1-carboxylic acid (ACC), promoted the formation of spermatangia and parthenosporangia in male and female gametophytes, respectively, of the dioecious species Pyropia pseudolinearis. In addition, we determined expression profiles of ACC-responsive genes in the gametophytes during sexual reproduction using RNA-Seq and quantitative real-time PCR (qRT-PCR). Genes involved in the regulation of cell division and cell wall organization, such as high-mobility group (PpHMG) and glycosyltransferase family (PpGT14), were found to be upregulated in male and female gametophytes treated with ACC. In addition, the relatively rapid ACC-response of the vesicular-trafficking-related genes, flotillin (PpFLOT), charged multivesicular body protein 5 (PpCHMP5), and peptidase family S8 (PpS8) was shown to occur during male and female sexual reproduction. Expression levels of these six genes in the monoecious species P. yezoensis, which are homologs to ACC-responsive genes in P. pseudolinearis, also increased in gametophytes treated with ACC. These findings could provide new insights into the ACC-regulation of the sexual life cycle in Pyropia species.
  • Characterization and expression profiles of small heat shock proteins in the marine red alga Pyropia yezoensis
    T. Uji, Y. Gondaira, S. Fukuda, H. Mizuta, N. Saga
    Cell Stress and Chaperones 24 223 - 233 2019年01月10日 [査読有り]
  • Shimizu K, Uji T, Yasui H, Mizuta H
    Journal of Applied Phycology 30 2 1371 - 1379 2018年 [査読有り][通常論文]
     
    In this study, the oligoguluronate elicitor-induced oxidative burst (OB) was monitored continuously in young and mature Saccharina japonica sporophytes based on luminol chemiluminescence using a photon counter. The iodoperoxidase (IPO) activity, abscisic acid (ABA), and polyphenol contents were also compared in the different growth stages. The elicitor-induced OB occurred within 1 min and reached its maximum in 15-20 min after treatment in all growth stages. The active elicitor-induced OB was stronger in the young sporophytes than the older sporophytes. The IPO activity in the different growth stages also exhibited a similar pattern to the elicitor-induced OB. These results suggest that the elicitor-induced OB and the subsequent high haloperoxidase activity comprise a major defence mechanism in young sporophytes. By contrast, ABA accumulated with the growth of the sporophytes. Interestingly, ABA treatment suppressed the elicitor-induced OB during growth and enhanced the elicitor-independent IPO activity even in the young sporophytes. In addition, the polyphenol content was higher in the older sporophytes than the younger sporophytes. These observations show that dramatic changes occur in the characteristic defences against biotic stresses as the sporophyte grows, as well as suggesting that ABA is closely linked with these changes. Moreover, the IPO activity recovered slightly in the sorus, which is the reproductive tissue, thereby suggesting that a higher ABA content increases the defence activity and the success of reproduction.
  • Toshiki Uji, Ryuya Matsuda, Katsuaki Takechi, Hiroyoshi Takano, Hiroyuki Mizuta, Susumu Takio
    JOURNAL OF APPLIED PHYCOLOGY 28 6 3501 - 3509 2016年12月 [査読有り][通常論文]
     
    Plant growth regulators (PGRs) play a pivotal role in vascular plants, regulating growth, development, and stress responses; however, the role of PGRs in algae remains largely unexplored. Here, the role of ethylene, a simple plant growth regulator, was demonstrated in sexual reproduction of the marine red alga Pyropia yezoensis. Application of the ethylene precursor 1-aminocylopropane-1-carboxylic acid (ACC) promoted the formation of spermatia and zygotospores in the gametophytes as well as ethylene production, whereas the growth rate was repressed in comparison to gametophytes not treated with ACC. In addition, gametophytes treated with ACC and mature gametophytes showed enhanced tolerance to oxidative stress. Gene expression profiles revealed upregulation of genes involved in cell division and stress response in gametophytes treated with ACC and in mature gametophytes. These results indicate that ethylene plays an important role in the regulation of gamete formation and protection against stress-induced damage during the sexual reproductive stage. Considered together, these findings demonstrate that ethylene is involved in regulating the switching from a vegetative to a sexual reproductive phase in P. yezoensis.
  • 谷敬志, 川越力, 松本世津子, 水田浩之, 安井肇
    水産増殖 63 3 235 - 244 日本水産増殖学会 2015年 [査読有り][通常論文]
     
    函館市根崎沿岸において，ガゴメの季節的消長と形態形成について詳細に観察した。その結果，1～7月に発生したガゴメの1年目幼胞子体は10月までゆっくりと生長して約10 cm になり，10月～翌年1月に全てが再生した。再生現象が見られるまでに成熟する胞子体は見られなかった。2年目胞子体は1～7月の期間，著しい生長を示し7月には葉長が 2 m を超える大形体となった。8～10月には腐朽が見られ，約100 cm となるが10～11月に成熟した。標識をつけた2年目胞子体400個体のうち，約40%の胞子体で12月～翌年2月に再生が確認されたがほとんどが4月までに流失し，7月まで生長した胞子体は400個体のうち約2%だけであった。3年目胞子体は8～10月に腐朽したが10～11月には成熟した。その後，12月には全ての胞子体が流失した。
  • Ryo Hirata, Toshiki Uji, Satoru Fukuda, Hiroyuki Mizuta, Asao Fujiyama, Satoshi Tabata, Naotsune Saga
    JOURNAL OF APPLIED PHYCOLOGY 26 4 1863 - 1868 2014年08月 [査読有り][通常論文]
     
    Genetic transformation systems using reporter genes in whole plants have a wide variety of applications for molecular biological study including the visualization of expression patterns of particular genes and intracellular biological phenomena as well as the identification of novel genes. In this study, we assessed co-expression of each three codon-optimized reporter genes and a selectable marker in the nuclear transformation system of whole Pyropia yezoensis, a red marine alga. With the use of an endogenous promoter, both the codon-optimized hygromycin resistance gene and -glucuronidase gene (PyGUS) were co-expressed in P. yezoensis cells. A high level of GUS activity was observed in 60 % of the individuals in hygromycin-resistant lines. A histochemical GUS assay revealed that the PyGUS reporter gene was stably introduced and expressed throughout the algae's life cycle. In addition, two live cell reporters, humanized cyan fluorescent protein from Anemonia majano and luciferase from Gaussia princeps, were successfully expressed in whole P. yezoensis. The development of this transformation system involving three types of reporter genes provides opportunities for monitoring temporal changes in gene expression and for genetic screening in red marine algae.
  • Toshiki Uji, Ryo Hirata, Satoru Fukuda, Hiroyuki Mizuta, Naotsune Saga
    MARINE BIOTECHNOLOGY 16 3 251 - 255 2014年06月 [査読有り][通常論文]
     
    Marine macroalgae play an important role in marine coastal ecosystems and are widely used as sea vegetation foodstuffs and for industrial purposes. Therefore, there have been increased demands for useful species and varieties of these macroalgae. However, genetic transformation in macroalgae has not yet been established. We have developed a dominant selection marker for stable nuclear transformation in the red macroalga Pyropia yezoensis. We engineered the coding region of the aminoglycoside phosphotransferase gene aph7aEuro(3) from Streptomyces hygroscopicus to adapt codon usage of the nuclear genes of P. yezoensis. We designated this codon-optimized aph7aEuro(3) gene as PyAph7. After bombarding P. yezoensis cells with plasmids containing PyAph7 under the control of their endogenous promoter, 1.9 thalli (or individuals) of hygromycin-resistant strains were isolated from a 10-mm square piece of the bombarded thallus. These transformants were stably maintained throughout the asexual life cycle. Stable expression of PyAph7was verified using Southern blot analysis and genomic PCR and RT-PCR analyses. PyAph7 proved to be a new versatile tool for stable nuclear transformation in P. yezoensis.
  • Toshiki Uji, Rei Sato, Hiroyuki Mizuta, Naotsune Saga
    JOURNAL OF APPLIED PHYCOLOGY 25 6 1887 - 1893 2013年12月 [査読有り][通常論文]
     
    Multiprotein bridging factor 1 (MBF1) is a highly conserved transcriptional co-activator involved in the regulation of diverse processes, such as environmental stress responses. We recently identified a novel MBF1 gene, PyMBF1, from the marine red alga Pyropia yezoensis. In this study, quantitative real-time PCR analysis revealed that PyMBF1 transcripts were upregulated in P. yezoensis cells during exposure to oxidative and heat stresses. We also examined heat signaling in P. yezoensis cells by monitoring the accumulation of PyMBF1 transcripts. Heat activation of PyMBF1 was inhibited by the membrane rigidifier dimethylsulfoxide, whereas it was induced without heat stress by the membrane fluidizer benzyl alcohol (BA). Induction of PyMBF1 transcripts by heat and BA was inhibited by 1-butanol, an inhibitor of phospholipase D (PLD). The results suggest that the heat activation of PyMBF1 requires membrane fluidization and activation of PLD. These findings provide an initial step toward understanding heat signaling in marine red algae.
  • Yang Liu, Sei-Ichi Saitoh, I. Nyoman Radiarta, Tomonori Isada, Toru Hirawake, Hiroyuki Mizuta, Hajime Yasui
    ICES JOURNAL OF MARINE SCIENCE 70 7 1460 - 1470 2013年11月 [査読有り][通常論文]
     
    Japanese kelp (Saccharina japonica) is one of the most valuable cultured and harvested kelp species in Japan. In this study, we added a physical parameter, sea surface nitrate (SSN) estimated from satellite remote sensing data, to develop a suitable aquaculture site-selection model (SASSM) for hanging cultures of Japanese kelp in southern Hokkaido, Japan. The local algorithm to estimate SSN was developed using satellite measurements of sea surface temperature and chlorophyll-a. We found a high correlation between satellite-and ship-measured data (r(2) = 0.87, RMSE = 1.39). Multi-criteria evaluation was adapted to the SASSM to rank sites on a scale of 1 (least suitable) to 8 (most suitable). Wefound that 64.4% of the areas were suitable (score above 7). Minamikayabe was identified as the most suitable area, and Funka Bay also contained potential aquaculture sites. In addition, we examined the impact of El Nino/La Nina-Southern Oscillation (ENSO) events on Japanese kelp aquaculture and site suitability from 2003-2010. During El Nino events, the number of suitable areas (scores 7 and 8) decreased significantly, indicating that climatic conditions should be considered for future development of marine aquaculture.
  • Toshiki Uji, Hiroyuki Mizuta, Naotsune Saga
    MARINE BIOTECHNOLOGY 15 2 188 - 196 2013年04月 [査読有り][通常論文]
     
    The life cycle of plants entails an alternation of generations, the diploid sporophyte and haploid gametophyte stages. There is little information about the characteristics of gene expression during each phase of marine macroalgae. Promoter analysis is a useful method for understanding transcriptional regulation; however, there is no report of promoter analyses in marine macroalgae. In this study, with the aim of elucidating the differences in the transcriptional regulatory mechanisms between the gametophyte and sporophyte stages in the marine red alga Porphyra yezoensis, we isolated the promoter from the sporophyte preferentially expressed gene PyKPA1, which encodes a sodium pump, and analyzed its promoter using a transient gene expression system with a synthetic beta-glucuronidase (PyGUS) reporter. The deletion of -1432 to -768 relative to the transcription start site resulted in decreased GUS activity in sporophytes. In contrast, deletion from -767 to -527 increased GUS activity in gametophytes. Gain-of-function analyses showed that the -1432 to -760 region enhanced the GUS activity of a heterologous promoter in sporophytes, whereas the -767 to -510 region repressed it in gametophytes. Further mutation and gain-of-function analyses of the -767 to -510 region revealed that a 20-bp GC-rich sequence (-633 to -614) is responsible for the gametophyte-specific repressed expression. These results showed that the sporophyte-specific positive regulatory region and gametophyte-specific negative regulatory sequence play a crucial role in the preferential expression of PyKPA1 in P. yezoensis sporophytes.
  • Development of self-reliant bio-farming system by employing natural energy.
    Kimura N, Fujimori Y, Yasui H, Mizuta H, Abe T. Adachi, S, Takahashi Y
    FFTC Extension Bulletin 661 1 - 10 2013年 [査読有り][通常論文]
  • Hiroyuki Mizuta, Hajime Yasui
    JOURNAL OF APPLIED PHYCOLOGY 24 5 1177 - 1182 2012年10月 [査読有り][通常論文]
     
    We investigated biogenic silica deposition in sporophytes of kelp, Saccharina japonica (Laminariaceae). Silicon content was measured in different sporophyte regions and there was a trend for the silicon content to increase longitudinally from the stipe-blade transition to apical regions. The transverse trend was for the content to be higher in the marginal region than in the medial region. The silicon content was also higher in the scar and sorus regions compared with the adjacent vegetative regions. High silicon content was detected in the margin of the disc and in the sorus region of cultured sporophyte discs. Moreover, rhodamine 123 staining suggested that silicon was deposited in the mouth of the marginal wound of the disc. Rhodamine 123 fluorescence was also detected in the paraphyses and mucilaginous caps of sori. These results suggest that silicon plays important roles in tissue protection and vegetative tissue wound healing. It is also suggested that silicon is required for the protection of reproductive tissues. We also discuss the physiological and ecological roles of biogenic silica deposition in kelp and its management in cultivated fields.
  • Toshiki Uji, Ryota Monma, Hiroyuki Mizuta, Naotsune Saga
    FISHERIES SCIENCE 78 5 985 - 991 2012年09月 [査読有り][通常論文]
     
    Na+/H+ antiporters are known to play a crucial role in pH and Na+ homeostasis. In the present study, we characterized the molecular structures and expression patterns of two Na+/H+ antiporters from the marine red alga Porphyra yezoensis (designated PySOS1 and PyNhaD). The full-length cDNAs of PySOS1 and PyNhaD were 5122 and 1804 bp, and contained open reading frames (ORFs) of 4773 and 1275 bp, respectively. The deduced amino acid sequences showed high similarity to SOS1 and NhaD from the higher plant Arabidopsis thaliana. PySOS1 and PyNhaD contained conserved sequences found in the cation-proton antiporter. Quantitative real-time PCR analysis revealed that both antiporter genes were expressed in both the gametophyte and sporophyte of P. yezoensis. In addition, mRNA expression of PySOS1 and PyNhaD was simultaneously upregulated by light irradiation, suggesting that coordinated activity between the two is important in pH and Na+ homeostasis under light conditions. Moreover, the expression levels of both genes were partially reduced by the photosynthetic inhibitors DCMU and DBMIB, suggesting that upregulation is linked to photosynthesis-related metabolism. These findings provide an initial step towards understanding Na+/H+ antiporters in marine red algae.
  • Miwa Kanamori, Hiroyuki Mizuta, Hajime Yasui
    JOURNAL OF APPLIED PHYCOLOGY 24 4 701 - 706 2012年08月 [査読有り][通常論文]
     
    Explants obtained from young sporophytes of Saccharina japonica were cultured in an artificial medium with different concentrations of Ca2+ (0-20 mM). The culture with 10 mM Ca2+ promoted the formation of unpigmented filamentous callus-like cells in the cortical layer. In contrast, explants cultured with 5 mM Ca2+ formed pigmented round callus-like cells in the epidermis at a high percentage. The thallus regeneration rate of explants in 5 mM Ca2+ was ten times higher than those of explants cultured in 10 mM Ca2+. Ambient Ca2+ concentrations also influenced the production of radical oxygen species (ROS) in explants. Explants cultured in 10 mM Ca2+ produced higher ROS than did those cultured in 5 mM. The ROS production was histologically observed mainly in the plasma membrane of callus-like cells using 2', 7'-dichlorodihydrofluorescein diacetate. Moreover, a nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor, diphenyleneiodonium chloride, inhibited the ROS production with propagation of filamentous callus-like cells. These results suggest that Ca2+ concentration in medium influences the development of callus-like cells and thallus regeneration by affecting NADPH oxidase activity and ROS production in the plasma membrane of the callus-like cells. Therefore, the morphological form of callus-like cells and the development of thallus will be controlled by Ca2+ concentration in the medium.
  • Takahashi Megumu, Mikami Koji, Mizuta Hiroyuki, Saga Naotsune
    Journal of Aquaculture Research & Development 2 4 4  OMICS Group 2011年 [査読有り]
     
    Despite the development of transient gene expression in red algae Porphyra species, a stable transformationsystem has not been established in these algae yet. One reason for the difficulty in the transformation is the lackof a way to select transformed cells from the algae. Thus, to identify antibiotics suitable for the selection of stablytransformed cells, we tested the gametophyte for sensitivity to 6 antibiotics, ampicillin (Am), kanamycin (Km),hygromycin (Hm), geneticin (G418), chloramphenicol (Cm) and paromomycin (Pm), which are frequently employedas selection agents in the transformation of land plants and microalgae. Sensitivity tests, which were carried out withdifferent concentrations (0-10 mg mL-1) of antibiotics, showed that Hm, G418, Cm and Pm exhibited a lethal effect atmore than 1.0 mg mL-1, suggesting the suitability of these four antibiotics for the selection of genetically transformedcells from P. yezoensis gametophytes, while P. yezoensis gametophytes were highly resistant to Am and Km. Wealso succeeded in reducing the antibiotic concentrations by lowering the pH value and salt concentration using anartificial synthetic medium. Increasing the sensitivity of gametophytic cells to Hm, G418, Cm and Pm in the modifiedsynthetic medium will contribute to establishing a genetic transformation system in P. yezoensis.
  • Hiroyuki Mizuta, Hajime Yasui
    BOTANICA MARINA 53 5 409 - 416 2010年10月 [査読有り][通常論文]
     
    We investigated production of radical oxygen species (ROS) in sorus development of sporophyte discs and during zoospore germination of Saccharina japonica (Phaeophyceae) using the fluorescent dye 2',7'-dichlorofluorescein diacetate (DCFH-DA). Quantitative analysis of ROS showed high intracellular production during the stages of zoosporangium formation when paraphyses elongated. In this stage, remarkable ROS release was observed. ROS production was also observed histologically (under a fluorescence microscope) in the elongating paraphyses and the sorus zoosporangia. The sorus had significantly higher phenol content, antioxidant capacity and ROS scavenging enzyme activities (ascorbate peroxidase, catalase, glutathione reductase and superoxide dismutase) than adjacent non-sorus blade sectors. Thus, intracellular ROS scavenging mechanisms are active during ROS production in sorus formation. In contrast, iodine content was lower in the sorus than in the adjacent non-sorus tissues, suggesting the existence of an antioxidant defense mechanism based on iodine efflux. We demonstrated that ROS production is an important phenomenon in the reproduction of the S. japonica sporophyte. Furthermore, ROS were also observed in the zoospore germination processes. We discuss the physiological and ecological roles of ROS production in sorus formation and zoospore germination.
  • Simple method for estimating fucoidan and laminaran contents in several brown algae
    Akita Y, Mizuta, H, Yasui, H
    Algal Resources 3 93 - 98 2010年 [査読有り][通常論文]
  • Katsuhiro Tabuchi, Hiroyuki Mizuta, Hajime Yasui
    AQUACULTURE RESEARCH 41 1 1 - 10 2009年12月 [査読有り][通常論文]
     
    The effects of 5-aminolevulinic acid (ALA) on the induction and growth of callus-like cells in Laminaria japonica were investigated in explants obtained from basal, middle and apical portions along the sporophyte. 5-Aminolevulinic acid treatment promoted the induction of callus-like cells in explants obtained from all portions, and the induction rate was higher when a concentration of 50-500 mg L-1 of ALA was used. The promotion was especially remarkable in apical explants, and the induction was 10-14 times higher in the 100-500 mg L-1 range than that in the 0 mg L-1. The cell division rate of callus-like cells showed the highest value in the explants cultured with 500 mg L-1 of ALA for 14 days. The promotion of the cell division rate by culturing with 500 mg L-1 ALA was also observed under white, blue and red lights. The callus-like cells, which were cultured in 500 mg L-1 of ALA for 2 months, had many clear chloroplasts. After 3 months, young thalli occurred. These results suggest that the ALA treatment is effective for stable propagation of callus-like cells in L. japonica.
  • Hirotoshi Endo, Eun-Jeong Park, Youichi Sato, Hiroyuki Mizuta, Naotsune Saga
    FISHERIES SCIENCE 75 2 393 - 400 2009年04月 [査読有り][通常論文]
     
    As a trial to develop a method of authenticating the place of origin of circulated Undaria pinnatifida products, we investigated their intraspecific genetic diversity using the mitochondrial cytochrome c oxidase subunit 1 gene (cox1) and the internal transcribed spacer 2 (ITS2) region of the nuclear ribosomal DNA (rDNA) sequence. Four dried U. pinnatifida products labeled with their origins (one from Japan, one from China and two from Korea), natural plants collected from three locations (two from Japan and one from China), and cultivated plants collected from two locations (one from Japan and one from China) were used in the present study. The amplified fragments of cox1 were 664 bp in length, and the aligned sequences were highly homologous. Among the nine sequences, no insertions or deletions were found and six substitution positions were detected, and they were classified into five haplotypes. In contrast, multiple highly variable regions were found in ITS2, and some of them carried a restriction site for Mbo II. Polymerase chain reaction-restriction fragment length polymorphism analysis showed different restricted profiles among the tested samples. The availability of molecular markers for authenticating food products of U. pinnatifida is discussed.
  • Ako Saito, Hiroyuki Mizuta, Hajime Yasui, Naotsune Saga
    AQUACULTURE 281 1-4 138 - 144 2008年09月 [査読有り][通常論文]
     
    A dioecious red alga, Porphyra pseudolinearis, which does not produce asexual spores such as archeospore, is a commercially valuable Porphyra seaweed. We obtained a large amount of regenerable free cells of P. pseudolinearia by gentle homogenization in seawater after culturing the thalli in nutrient-rich medium with 10 mM of allantoin at 15 degrees C and 20 degrees C. The obtained free cells were divided into three forms: globular, elliptic and 2-celled. These free cells formed cell walls slowly compared to conchospores, and they directly developed to thalli or filamentous germlings like conchocelis or conchosporangia. In particular, the occurrence of thalli was remarkable in free cells obtained from the thalli cultured with 10 mM allantoin at 20 degrees C. Once the free cells developed to the thalli, they showed the same rates of growth to the thalli generated from conchospores, and they grew to be more than 50 cm in blade length. This technique to produce regenerable free cells from the Porphyra species that do not produce archeospores is useful for vegetative propagation and breeding. (C) 2008 Elsevier B.V. All rights reserved.
  • 高橋 潤, 富松亮介, 遠藤博寿, 北出幸広, 水田浩之, 嵯峨直恆
    水産育種 37 1 19 - 27 水産育種研究会 2008年 [査読有り][通常論文]
  • Hiroyuki Mizuta, Tomoki Kai, Katsuhiro Tabuchi, Hajime YAsui
    AQUACULTURE RESEARCH 38 12 1323 - 1329 2007年09月 [査読有り][通常論文]
     
    Responses of the sporophytes of Laminaria japonica to blue, red and white lights were investigated using segments, discs and whole plants. The relative growth rate with regard to the blade's length and width showed no difference among the light conditions during 2 weeks of culturing. On the contrary, the elongation rates of the stipe and the holdfast were 1.7-2.5 times higher under red light than that under white light as a control. Callus formation in the segments was also promoted more under red light conditions than under white or blue light. Blue light irradiation resulted in a 48% and 12% decrease in the relative growth rate of the stipe and the holdfast, respectively, in comparison with the control. When sporophyte discs were cultured for 10 weeks, all discs formed zoosporangial sori 2-3 weeks earlier under blue light than under white light. However, red light inhibited the formation of zoosporangia. Indoleacetic acid (IAA) oxidase activity was about two-fold higher under blue light than under red light, suggesting that the difference in response between the blue and red light conditions is related to the internal IAA level of the tissues. The developmental, reproductive and morphological effects of blue and red lights will be useful for the artificial control of the life cycle of Laminaria plants and for the development of more efficient cultivation techniques.
  • 中田 和義, 山崎 友資, 水田 浩之, 川井 唯史, 伊藤 博, 五嶋 聖治
    水産増殖 54 3 375 - 381 水産増殖談話会 2006年09月 [査読有り][通常論文]
     
    北海道南西部の日本海沿岸で見られる藻場の消失に、植食性小型巻貝類が及ぼす影響を解明する上で必要となる基礎的知見を得ることを目的に、小型巻貝によるホソメコンブの摂食に水温が及ぼす影響を室内実験によって検討した。まず、コシダカガンガラを用いて、スライドグラスとスチロール樹脂製容器に着生させたホソメコンブ配偶体に対する摂食実験を、水温5℃、10℃、15℃の3条件下でおこなった。コシダカガンガラによる配偶体の摂食量は、水温が高いほど多くなる傾向が認められたが、低水温の5℃であっても、コシダカガンガラは配偶体を摂食した。次に、コシダカガンガラとクボガイを用いて、ホソメコンブの幼胞子体（葉長3cm 程度）に対する摂食実験を、水温10℃と15℃の2 条件下で実施した。クボガイでは、水温条件に関わらず幼胞子体に対する活発な摂食が認められたが、コシダカガンガラでは、幼胞子体への摂食はほとんど見られなかった。以上から、植食性小型巻貝によるホソメコンブ群落に対する影響は、水温条件と巻貝種によって異なる可能性が示唆された。
  • Takeshi Kumura, Hajime Yasui, Hiroyuki Mizuta
    FISHERIES SCIENCE 72 4 860 - 869 2006年08月 [査読有り][通常論文]
     
    Sporophyll formation in two alariaceous plants, Undaria pinnatifida and Alaria crassifolia, was studied in relation to the nutrient requirements. The sporophylls of U pinnatifida formed zoosporangia when they had N and P contents greater than 1.4 kgN/m(3) and 0.74 kgP/m(3). This indicates that these values are the critical nutrient levels for zoospore formation in U. pinnatifida. In the sporophytes of A. crassifolia, many sporophylls with zoosporangia showed nutrient contents higher than 6.25 kgN/m(3) and 1.70 kgP/m(3). These results suggest that the U. pinnatifida can form zoospores at lower levels of N and P contents than A. crassifolia. Both species often formed zoosporangial sori on the blades in the late period of each reproductive season. The fertile parts of the blade showed N and P contents higher than the critical levels. This phenomenon indicates that the blades have the capability to form zoosporangial sori if there is a sufficient accumulation of nutrients for zoospore formation. The zoospore formation on the blade seems to be accomplished by an overflow of excess nutrients from sporophylls into the blade, or by accumulating sufficient nutrients to form sori even if the sporophylls are not formed.
  • 中田 和義, 山崎 友資, 水田 浩之, 川井 唯史, 伊藤 博, 五嶋 聖治
    水産増殖 54 2 217 - 224 水産増殖談話会 2006年06月 [査読有り][通常論文]
     
    北海道南西部の日本海沿岸で見られる藻場の消失に、植食性小型巻貝類が及ぼす影響について調べる上で必要となる基礎的知見を得ることを目的に、研究を実施した。まず、小型巻貝4種（クボガイ、コシダカガンガラ、エゾサンショウ、クロタマキビ）によるホソメコンブに対する摂餌痕跡を室内実験で観察した。スチロール樹脂製容器とスライドグラスに着生させたホソメコンブの配偶体をこれら4種の巻貝に摂餌させたところ、すべての巻貝種で配偶体の摂餌が継続的に確認され、巻貝種間で特徴の異なる摂餌痕跡が観察された。この摂餌痕跡の種間差は、歯舌の形態と大きさや摂餌様式が巻貝種間で異なることが影響したと考えられた。次に、野外で採集したホソメコンブの胞子体を観察したところ、小型巻貝による歯舌の痕跡と思われる形跡が多数観察された。以上から、植食性小型巻貝がホソメコンブ群落に何らかの影響を与える可能性が示唆された。
  • Tomoki Kai, Kazumi Nimura, Hajime Yasui, Hiroyuki Mizuta
    JOURNAL OF APPLIED PHYCOLOGY 18 1 95 - 101 2006年02月 [査読有り][通常論文]
     
    Young sporophytes of Laminaria japonica Areshoug were cultured in six indole-acetic acid ( IAA) concentrations ( 0, 10(-8), 10(-7), 10(-6), 10(-5), 10(-4) M) to examine the effect of auxin on growth. The effects of auxin on sorus formation were also examined by using discs taken from the adult sporophyte. The auxin contents and IAA oxidase activities in the thallus and sorus parts of the sporophyte were determined with the blade and sporophyll of other Laminariales plants, Undaria pinnatifida ( Harvey) Suringar and Alaria crassifolia Kjellman. The young sporophytes of L. japonica showed highest elongation rate in 10(-5) MIAA. In contrast, the sorus formation on the discs cultured in 10(-5) MIAA was markedly delayed in comparison with other concentrations, indicating that sorus formation was suppressed by IAA. Free and conjugated auxin contents were lower in the reproductive parts than in the vegetative parts. In three Laminariales sporophytes, IAA oxidase activity was about 3-9 times higher in the reproductive parts than in the vegetative parts. Taken together these results suggest that the growth and reproduction of Laminariales sporophytes are regulated by internal auxin levels. Elucidating the regulation mechanism is likely to provide information that is important for the management of plant production and the assessment of the physiological status of plants in the field.
  • 川越 力, 谷 敬志, INDY Jeane Rimber, 水田 浩之, 安井 肇
    水産増殖 53 2 181 - 187 水産増殖談話会 2005年06月 [査読有り][通常論文]
     
    北方海域において、フシスジモクの計画的な増殖を展開する際に基礎となる育成技術を開発する目的で、異なる水温下で受精卵から幼体までの形態形成過程を明らかにし、幼胚、幼体生長に適した条件を決定した。2000年6月に江差町沿岸のフシスジモク群落より受精卵を採取し、光周期12h明期：12h暗期、光量40μE／m2／s、 水温3℃、5℃、10℃、15℃、20℃ で静置培養した。水温3℃では、7日後に1次仮根胚となり、その後発生は停滞した。水温5℃では、60時間後に1次仮根胚、10日後に2次仮根胚となり、発生が停滞した。水温10℃では、48時間後に1次仮根胚、7日後に2次仮根胚、1年後に主軸形成体となった。水温15℃では、36時間後に1次仮根胚、5日後に2次仮根胚、2カ月後に主軸形成体、3カ月後に付着器形成体、6カ月後に主枝形成体となった。水温20℃では、36時間後に1次仮根胚、3日後に2次仮根胚、1カ月半後に主軸形成体、3カ月後に付着器形成体、6カ月後に主枝形成体となったが、付着器形成体の段階で枯死する個体が見られた。以上から、水温15℃は北海道産フシスジモクの幼胚、幼体の生長に適していることがわかった。また、水温 3℃、5℃は幼胚を長期保存するのに適した水温であることを認めた。
  • 冨松亮介, 高橋潤, 遠藤博寿, 北出幸広, 水田浩之, 嵯峨直恆
    水産育種 34 2 123 - 128 水産育種研究会 2005年 [査読有り]
  • 森 俊介, 山崎 綾乃, 芹澤 松山, 福田 覚, 水田 浩之, 嵯峨 直恆
    水産増殖 52 3 239 - 244 水産増殖談話会 2004年09月 [査読有り][通常論文]
     
    スサビノリ無菌培養株を無菌状態で培養した藻体を対照実験系とし、共生細菌BPY-W6、BPY-W8を添加した株について、それぞれ葉長、葉幅を測定し、これらのデータに基づき葉面積、形態指標値を算出した。共生細菌BPY-W6、BPY-W8を添加した株の平均葉長・葉幅はどちらも対照実験株より大きかった。平均葉面積はBPY-W6を添加した株で121.4倍、BPY-W8を添加した株で76.8倍の大きさを示した。形態指標値より、BPY-W6を添加した株は卵形、BPY-W8を添加した株は楕円形に近い配偶体を形成する傾向が見られた。BPY-W6およびBPY-W8はともにスサビノリの成長に影響を及ぼすことがわかった。影響の度合は細菌株によって異なることが示唆された。
  • 水田 浩之
    沿岸海洋研究 41 1 33 - 38 The Oceanographic Society of Japan (OSJ) 2003年08月 [査読有り][招待有り]
     
    我が国におけるコンブ属植物の分布は北海道および本州北部に限られているが,沿岸親潮域に生育する種は,その生産量も高く産業的に重要な位置を占めている.一般的にコンブ属植物の分布域の違いは,水温に基づいて説明されている.本シンポジウムでは,北海道太平洋岸に分布するコンブ属植物4種について,胞子体の成熟における栄養要求特性と分布との関連性について考察した.その結果,親潮の影響を強く受ける海域に分布するナガコンブやミツイシコンブ(寒流系コンブ)の成熟部位は,高い栄養塩含有量を持っているにもかかわらず,低い繁殖努力を示した.これに対し,親潮の影響の少ない海域に分布するマコンブやホソメコンブ(暖流系コンブ)の成熟部位は,低い栄養塩含有量を持っているにもかかわらず,高い繁殖努力を示した.これらのことは,マコンブやホソメコンブは繁殖にかかるコスト(栄養要求量)を抑えることで,その環境での再生産を可能にしていると考えられる.
  • Hiroyuki Mizuta, Hajime Yasui, Naotsune Saga
    Journal of Applied Phycology 15 4 345 - 349 2003年07月 [査読有り][通常論文]
     
    A simple method is presented for obtaining a large number of monospores in the thallus of Porphyra yezoensis. The method implies two principles: induction of monosporangium formation by allantoin, and liberation of monospores from the cell wall by mild homogenization. The induction of monosporangium formation was accomplished by culturing wild thalli in nutrient-enriched seawater with 10 mM of allantoin for approximately 3 weeks. This high concentration (10 mM) of allantoin suppressed the growth of the thalli compared with lower concentrations (0-1 mM). Thalli cultured for 3 weeks were mildly homogenized with a glass homogenizer and the monospore solution was obtained by filtering with a nylon mesh. The monospores grew normally to thalli. This technique of monospore acquisition is a simple and useful method for the propagation and breeding of P. yezoensis thalli.
  • H Mizuta, S Ogawa, H Yasui
    AQUATIC BOTANY 76 2 117 - 126 2003年06月 [査読有り][通常論文]
     
    The relationship between phosphorus uptake and internal phosphorus status was studied on the kelp species, Laminaria japonica Areshoug. Elongation of the cultivated sporophyte ceased after June when phosphorus content was less than 1.3 mug P (g DW)(-1), indicating that this is the critical phosphorus content required for growth. The uptake rates of inorganic phosphorus, organic phosphorus, and extracellular alkaline phosphatase rapidly increased when the phosphorus content decreased to the critical level. These results suggest that phosphorus acquisition by the sporophyte is closely linked to the internal phosphorus level. Moreover, nucleic acid content correlated to the phosphorus content when the level of phosphorus was greater than the critical value, suggesting that the critical phosphorus content is a good indicator of phosphorus requirement and utilization within the plant. (C) 2003 Elsevier Science B.V. All rights reserved.
  • Y Fukuhara, H Mizuta, H Yasui
    FISHERIES SCIENCE 68 6 1173 - 1181 2002年12月 [査読有り][通常論文]
     
    The release of zoospores from zoosporangia in Laminaria japonica mainly occurred at night. The maximum swimming speed of the zoospores was observed immediately after release (similar to160mum/s), and then decreased with time. The zoospores exhibited clear chemotaxis to high concentrations of nitrate-N and phosphate-P. Only half of the zoospores were observed to swim against seawater with a flow velocity of 124 mum/s. The zoospores became floating spores after they stopped swimming in the seawater. Low light and low water temperature conditions prolonged the swimming period of the zoospores. However, the photosynthesis of the zoospores was suppressed in low water temperatures, and was also limited under high light irradiance. These results suggest that photosynthesis in zoospores does not prolong their swimming period, and that when their swimming energy is exhausted, floating spores appear.
  • K Nimura, H Mizuta
    JOURNAL OF APPLIED PHYCOLOGY 14 3 159 - 163 2002年06月 [査読有り][通常論文]
     
    The effects of exogenous abscisic acid (ABA; 10(-7)-10(-5) M), a known plant growth regulator, on reproduction and growth were investigated by culturing discs from sporophytes of Laminaria japonica Areschoug. ABA plays a role in triggering sorus formation, and it was found that sorus formation of discs was fastest in 10(-5) M ABA. The application of 10(-5) M ABA to culturing discs also suppressed the expansion of surface area. ABA contents in sorus and vegetative parts of the sporophyte were determined by bioassay. The mean ABA content in sorus parts obtained from sporophytes was 0.222 +/- 0.053 mug equivalent-ABA g wet weight(-1), which was about five times higher than the content found in vegetative parts (0.048 +/- 0.009 mug equivalent-ABA g wet weight(-1)). Taken together these results suggest that sorus development requires an elevated level of ABA and is associated with decreasing vegetative growth and that the ABA level of the sporophyte may play a crucial role in reproduction.
  • 二村 和視, 水田 浩之
    水産増殖 50 2 157 - 162 水産増殖談話会 2002年06月 [査読有り][通常論文]
     
    マコンプの子嚢斑形成について胞子体から得た藻体片を培養し、子嚢斑形成様式を調べた。鉛直的に切り出した藻体片ではそれらの基部側に子嚢斑が形成された。一方、水平に切り出した藻体片においては、縁辺部と基部の移行部に子嚢斑が形成された。中帯部と縁辺部を切り離し培養した結果、中帯部では基部側から成熟し、縁辺部では中帯部側に子嚢斑が形成された。子嚢斑が形成される部位は栄養塩が蓄積しやすいシンク(供給先)に相当する。子嚢斑の形成部位は胞子体内での栄養塩の移動が関与していると推察した。
  • K Nimura, H Mizuta, H Yamamoto
    BOTANICA MARINA 45 2 184 - 188 2002年03月 [査読有り][通常論文]
     
    The critical contents of nitrogen and phosphorus for sorus formation in Laminaria angustata, L. japonica, L. ochotensis and L. religiosa were measured using cultured discs cut from the sporophytes. In L. japonica, fertile sporophytes were also used. Discs were cultured in Provasoli's enriched seawater or nutrient-poor seawater at 10 degreesC under 100 mumol photons m(-2) s(-1) of irradiance (12L:12D). Regardless of the nutrient conditions in the culture media, the contents of nitrogen and phosphorus in the sorus part of discs and sporophytes of L. japonica were above 1.78 mg N cm(-3) and 0.19 mg P cm(-3) respectively, showing these values are critical for sorus formation in this species. Discs of L. angustata, L. ochotensis and L. religiosa in PES had higher contents of nitrogen and phosphorus in sorus parts than in L. japonica. The sorus area increased with accumulation of nitrogen or phosphorus in all species, but in L. angustata it was small despite the high contents of nitrogen and phosphorus, showing that this alga has a high nutritional cost in reproduction that might be a physiological adaptation to cold and nutrient-rich habitats.
  • Relationship between phycoerythrin and nitrogen content in Gloiopeltis furcata and Porphyra yezoensis
    Mizuta, H, Shirakura, Y, Yasui, H
    Algae 17 89 - 93 2002年 [査読有り][通常論文]
  • A Ozaki, H Mizuta, H Yamamoto
    FISHERIES SCIENCE 67 3 415 - 419 2001年06月 [査読有り][通常論文]
     
    The nutrient uptake kinetics of Kjellmaniella crassifolia and Laminaria japonica were determined under a variety of conditions. The nitrate and phosphate uptake rates followed Michaelis-Menten kinetics toward ambient nutrient concentrations, showing no difference between the maximum uptake rates of the two species. However, half-saturations of nitrate and phosphate uptake kinetics in K. crassifolia were higher than those in L. japonica. Low water temperature (5 degreesC) greatly restrained the nitrate and phosphate uptakes of both algae. Low irradiance (< 100 muE/m(2) per s) restrained nitrate and phosphate uptakes only in L. japonica, although high irradiance (> 100 muE/m(2) per s) caused no difference between the two species. The nitrate and phosphate uptake rates at low irradiance in K. crassifolia were 2-7 times higher than those in L. japonica. Light compensation and saturation irradiances in K. crassifolia were significantly lower than in L. japonica. These results indicate that K. crassifolia is able to take up carbon and nutrients at low irradiance, which suggests that the nutrient uptake characteristic of K. crassifolia could allow it to adapt to deeper habitats and even to high water turbidity.
  • 水田 浩之, 鳴海 日出人, 山本 弘敏
    水産増殖 49 2 175 - 180 水産増殖談話会 2001年06月 [査読有り][通常論文]
     
    ホソメコンブの遊走子を異なる硝酸態窒素（0～100μM）およびリン酸態リン濃度（0～100μM）の人工海水中で培養し、生長や成熟に及ぼす影響を調べた。雌性配偶体は硝酸およびリン濃度がそれぞれ5.0μM、1.0μM以上の場合に成熟し、胞子体を形成した。この濃度は配偶体世代から胞子体世代へ移行する際の閾値を示している。しかし、これは窒素とリンの制限を同時に受けている場合の値であり、どちらか一方が十分に供給されると、それぞれの閾値は1.0μM、0.5μMへ低下した。このことは、閾値は制限する栄養塩が複数の場合、その相乗作用によって変動することを示している。また、貧栄養海水および5段階の栄養塩添加海水中で光量（0.76、7.74and14.8μE/m2/s）および水温（5～15℃）の影響を調べたところ、貧栄養あるいは低光量がそれぞれ単独に配偶体の生長・成熟を遅らせた。この結果は、栄養塩の体内への蓄積と積算光量がホソメコンブの配偶体の生長・成熟を制御していることを示している。
  • Ichiki, S, Mizuta, H.. Yasui, H, Yamamoto, H
    Bull. Fac. Fish. Hokkaido Univ. 52 2 103 - 109 北海道大学 2001年 [査読無し][通常論文]
  • Differences in photosynthesis and nucleic acid content between sterile and fertile parts of the sporophyte of Laminaria japonica (Phaeophyceae)
    Nimura, K, Mizuta, H
    Algae 16 151 - 155 2001年 [査読有り][通常論文]
  • S Ichiki, H Mizuta, H Yasui, H Yamamoto
    PHYCOLOGIA 39 5 408 - 415 2000年09月 [査読有り][通常論文]
     
    Nonnucleate, uninucleate. binucleate, trinucleate and tetranucleate spores were found in sporophytes of Lithophyllum yes soense. The formation of polynucleate spores was caused mainly by the irregular distribution of nuclei in tetrasporangia. Both nuclei in a binucleate spore took part in development, suggesting that polynucleate spores grow into chimaeric crusts. The relative growth rate was higher in sporelings developed from trinucleate and tetranucleate spores (c. 12% d(-1)) than from uninucleate and binucleate spores (c. 5% d(-1)). However, the survival rates of sporelings developed from trinucleate and tetranucleate spores were less than half of those developed from uninucleate and binucleate spores. Polynucleate spores frequently occurred at low water temperature, especially at less than 12.1 degreesC. indicating that successful reproduction via spores would be limited by low water temperature in winter, although this is when spore production is highest in southwestern Hokkaido.
  • Shigeo Ichiki, Hiroyuki Mizuta, Hirotoshi Yamamoto
    Phycological Research 48 2 115 - 120 2000年 [査読有り][通常論文]
     
    Lithophyllum yessoense Foslie is a markedly dominant subtidal, crustose coral line alga in south-western Hokkaido, Japan. In this study, the effects of irradiance, water temperature and nutrients (nitrate and phosphate) on the growth of sporelings of the alga were examined. The relative growth rate (RGR) was saturated at 17.6% d-1 at a high irradiance (240 μmol photon m-2 s-1). Even at a low irradiance (10.7-49.9 μmol photon m-2 s-1), RGR was 7.1-12.7% d-1. The survival rate of sporelings was greater than 80% at irradiance above 10.7 μmol photon m-2 s-1 throughout the culture period. The growth of L. yessoense sporelings was promoted at 15°C and 20°C, but inhibited at 5°C. The half-saturation constants (Ks) for growth were about 0.5 μmol L-1 and 0.14 μmol L-1 for nitrate and phosphate, respectively. Saturated nitrate and phosphate concentrations for the growth were about 4.0 μmol L-1 and 0.4 μmol L-1, respectively, suggesting that L. yessoense is adaptable to a relatively high water temperature, a wide range of irradiance, and low ambient nitrate and phosphate concentrations. The results provide a possible explanation of why L. yessoense is dominant in the environments of south-western Hokkaido.
  • H Mizuta, K Nimura, H Yamamoto
    FISHERIES SCIENCE 65 1 104 - 108 1999年02月 [査読有り][通常論文]
     
    Optimal conditions for sorus formation of Laminaria japonica were investigated by culturing discs of the sporophyte in bottles. All discs formed sori in the seven combinational conditions of temperature (5-15 degrees C), irradiance (33.2-11.6 mu E.m(-2).s(-1)) and photoperiods (16:8, 12:12 and 8:16 h LD) in nutrient-rich medium. Sorus formation occurred earlier at 15 degrees C than at 5 and 10 degrees C and were largest in the area at 15 degrees C. Sori grew larger under high irradiance (116 mu E.m(-2).s(-1)) than under low irradiances (66.4 and 33.2 mu E.m(-2).s(-1)), but the initiation of sorus formation was not influenced by irradiance. Sorus formation was earlier in 8:16 h LD than in 12:12 and 16:8 h LD. Rapid formation of large sori occurred at high temperatures even in a long photoperiod. Sorus formation in discs in nutrient-poor medium was slower than that in discs in nutrient-rich medium, in which all discs formed large sori. Most discs in nutrient-poor medium formed very small sori. These results indicate that water temperature and nutrient conditions strongly affect both to the induction and expansion of sorus formation.
  • H Mizuta, K Nimura, H Yamamoto
    JOURNAL OF APPLIED PHYCOLOGY 11 6 585 - 591 1999年 [査読有り][通常論文]
     
    Sorus formation on median and marginal parts of Laminaria japoncia Areschoug was investigated by cultivating sporophytes from December 1996 to September 1997 in Southern Hokkaido, Japan. Simultaneously, discs (ca. 3 cm in diameter) that were cut off monthly from median and marginal parts of the cultivated sporophytes were incubated in our laboratory. All the cultivated sporophytes formed sori on the median parts from January to August, while all the median and marginal discs formed sori at 10 degrees C at 46 mu mol photon m(-2)s(-1) (12L:12D) in enriched medium. There was no difference in sorus area between median and marginal discs. These results indicated that the marginal parts are able to produce sori, although the greater part of them are actually washed away before forming sori in the sea. The marginal part is probably in a state of 'resource limitation' on the reproduction because the resource outflowed from this part to the basal part for the growth of sporophytes.
  • H Mizuta, J Hayasaki, H Yamamoto
    FISHERIES SCIENCE 64 6 909 - 913 1998年12月 [査読有り][通常論文]
     
    Seasonality of reproduction in sporophytes of Laminaria japonica was investigated on the basis of the nitrogen content of thalli cultivated in the field in southern Hokkaido, Japan. Fertile plants occurred throughout most of the year. Sorus formation was greatest in the basal parts of thalli in fall (September). The secondary peak of sorus formation occurred in the apical parts of thalli in winter (February and March). The seasonality of sorus formation was linked closely to the nitrogen content in the thalli. The nitrogen content per volume of thalli declined from January to April and then increased to a maximum in September. In January and February, the nitrogen content was higher in the apical part (ca. 2 mg.cm(-3)) than in the basal part of thalli. After June, however, it was higher in the basal part. Sorus area increased in association with the nitrogen content per volume of thalli regardless of the thallus part or season. In addition, although sorus formation took more than 100 days after April, it needed only about 50 days in February. These results suggest that the low nitrogen content in summer delayed sorus formation and decreased the area of the sori. The onset and position of sorus formation depended on the growth and the nitrogen content per volume of each thallus.
  • H Mizuta, K Torii, H Yamamoto
    FISHERIES SCIENCE 63 4 553 - 556 1997年08月 [査読有り][通常論文]
     
    Relations among carbon and nitrogen contents, photosynthetic capacity and surface-to-volume ratio were investigated using the discs cut from sporophytes of Laminaria japonica Areschoug. The relation between the carbon and nitrogen contents was divided into three phases on the basis of two distinctive nitrogen content levels, namely the subsistent and critical values. The first phase was characterized by a positive correlation between carbon and nitrogen amounts when nitrogen level was above the critical value (2.1% of dry weight). In the second phase, when nitrogen content decreased from 2.1% to 1.3% of the subsistent content, the correlation between carbon and nitrogen levels was negative. During the last phase, when the nitrogen content decreased below the subsistent value, carbon accumulation stopped. On the contrary, the photosynthetic activity of sporophytes under optimal conditions was severely suppressed when the nitrogen content fell below the subsistent value. Nitrogen levels above the subsistent value resulted in the linear increase in photosynthetic activity. In addition, the surface-to-volume ratio was correlated to the photosynthetic activity. These results indicate that photosynthetic capacity, carbon content and tissue size are linked to the nitrogen status, thus suggesting that the critical and subsistent nitrogen contents are helpful indicators for elucidating the productivity of sporophytes.
  • MIZUTA Hiroyuki, ICHIKI Shigeo, YAMAMOTO Hirotoshi
    Fishereis Science 63 5 721 - 724 1997年 [査読有り][通常論文]
     
    Viability of crustose coralline algae was measured using three oxidation-reduction indicators: 2,3,5-triphenyl tetrazolium chloride (TTC), 3-(4,5-dimethyl-tiazolyl-2)-2,5-diphenyl tetrazolium chloride (MTT) and alamar blue. The two tetrazolium salts, TTC and MTT, were reduced to form colored formazan in living corallines, but were not reduced in dead corallines. These formazans were extracted and quantified spectrophotometrically. Bluish violet MTT-formazan could be distinguished easily from red phycoerythrin and was useful for judging the viability of crustose corallines. Alamar blue indicated the viability visually and spectrophotometrically by changing the color of the culture medium. The alamar blue assay did not cause any damage to the growth of crustose corallines, indicating that it is suitable for estimating the viability of an individual plant over time. These results suggested that MTT and alamar blue can be used for rapid and simple assay in ecological and physiological investigations for crustose corallines.
  • MIZUTA Hiroyuki, MAITA Yoshiaki, HASHIMOTO Shinji
    Fisheries Science 62 2 161 - 167 1997年 [査読有り][通常論文]
     
    The nitrogen transportation within the thallus of Laminaria japonica Areschoug was investigated both in laboratory and field experiments. In the laboratory, it was observed by using N-15 as a tracer that the thallus allocated labelled soluble organic N to the younger basal tissues and labelled ammonium to the mature apical tissues. In addition, the younger basal tissues had a higher NH4+ uptake rate than mature apical tissues, and the assimilation of NH4+ was more active in the mature tissues. These results suggest that this transportation is based on two source-sink relationships. One is the transport of inorganic N from basal to mature tissues for assimilation. Another is the transport of soluble organic N assimilated in mature tissues to basal meristematic tissues for growth. To understand the transportation in the natural environment, tissue removal experiments were conducted during N-rich (Jan-Feb) and N-poor (Apr-May) periods. During N-rich periods, the removal of the apical parts led to a decrease of total soluble N content and an increase of inorganic N content in basal tissues and was associated with reduced growth rate. On the other hand, the removal of the basal part resulted in the reverse phenomenon to the removal of the apical part. Thus, the defined transport mechanism is closely connected with the younger basal tissues and mature apical tissues. It is suggested that the mechanism plays an important role in the growth and survival of the blade in the natural environment. The characteristics of the N transport mechanism are also discussed.
  • H MIZUTA, Y MAITA, K KUWADA
    FISHERIES SCIENCE 60 6 763 - 767 1994年12月 [査読有り][通常論文]
     
    The nitrogen status in the thallus of Laminaria japonica Areschoug under nitrogen limitation is divided to two phases, slight and serious N-deficient phases. This is done by judging from the quantitative storage levels of the soluble nitrogen in the tissues. The slight N-deficient phase is represented by the consumption of soluble nitrogen compounds in the storage pools. After the exhaustion of the nitrogen storage pools, the nitrogen status changes from a slight N-deficient phase to a serious N-deficient phase. Then catabolism was progressed and NH4+ was accumulated as a catabolite under the serious N-deficient phase. The treatment of L-methionine-DL-sulfoxisimine, an inhibitor of glutamine synthetase (GS), resulted in a considerably higher NH4+ accumulation within the tissue segments rather than non-treatment. This fact suggests the presence of a nitrogen recycling mechanism that the NH4+ produced from catabolic processes is actively re-assimilated by GS in the apical tissues. In the natural environment, the blade length was negatively correlated to an NH4+ content in apical tissues along the thallus during the serious N-deficient phase. This suggests that the nitrogen recycling mechanism may be an important role for survival of the seaweed in the period of N-deficiency in seawater. In addition, this mechanism may be closely related to the erosion of apical tissues that is called ''Suegare'' in Japan. Furthermore, the inducing mechanism of ''Suegare'' is also discussed considering with the nitrogen recycling mechanism in the thallus under the serious N-deficiency.
  • Phytoplankton carbon biomass estimated from the size-fractionated chlorophyll a concentration and cell density in the northern coastal waters from spring bloom to summer.
    Odate, T, Yanada, M, Mizuta, H, Maita, Y
    Bull. Plankton Soc. Japan 39 127 - 144 1993年 [査読有り]
  • Mizuta Hiroyuki, Maita Yoshiaki, Yanada Mitsuru
    日本水産学会誌 58 12 2345 - 2350 日本水産學會 1992年12月 [査読有り][通常論文]
     
    The seasonal changes of nitrogen metabolism in the sporophyte of Laminaria japonica (Phae-ophyceae) were investigated under a natural environment. The experiment was conventionally distinguished by concentrations of nitrogen compounds dissolved in seawater, that is, a relatively high NO2-+NO3- concentration period and a low one. In the high-nitrogen period, the prominent nitrogen metabolism was nitrogen uptake, assimilation, and accumulation. After the ambient nitrite+nitrate was exhausted from the seawater, the nitrogen metabolism was displaced to the utilization of the stored nitrogen. Wh...
  • Mizuta Hiroyuki, Maita Yoshiaki
    北海道大學水産學部研究彙報 42 3 107 - 114 北海道大学 1991年08月 [査読無し][通常論文]
  • Maita, Y, Mizuta, H, Yanada, M
    Bull. Fac. Fish. Hokkaido Univ. 42 98 - 106 1991年 [査読無し][通常論文]

MISC

講演・口頭発表等

所属学協会

  • 日本応用藻類学会   日本水産増殖学会   日本藻類学会   日本水産学会   

共同研究・競争的資金等の研究課題

  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2020年04月 -2023年03月 
    代表者 : 水田 浩之
     
    コンブ胞子体（巨視的世代）は、ストレスを受けると活性酸素を生産し様々な防御機構を誘導することが知られている。その一つとして、胞子体にはオキシダティブバーストによって誘導されるケイ素の細胞外取り込み機構が存在し、この機構が微小世代である配偶体にも備わっていることが示唆された。ケイ素の細胞外取り込み機構は、過酸化水素とハロペルオキシダーゼの存在下でポリフェノールとケイ素が架橋形成することで細胞壁の強化を図っているものと考えられ、配偶体のストレス防御機構の一端が明らかになった。 また、配偶体が他の藻類の下草等として生存・越年する状況を想定し、配偶体を5℃、遮光下で、培地の交換をせずに1～16カ月保存培養し、生残率を測定した。その後保存配偶体を10℃、白色光下（5-10 μmol photons m-2 s-1, 12hr明暗周期）で培養し、成長・成熟過程を観察した。さらに配偶体のクロロフィル蛍光パラメーター（Fv/Fm、Y(Ⅱ)、rETR、NPQ）を、パルス変調クロロフィル蛍光測定装置を用いて測定した。その結果、1‐3カ月間保存した配偶体は保存前と同様の細胞観を呈し、80%以上の生残率と一定のFv/FmとNPQ値を維持し、正常に成長・成熟する能力を有することが明らかになった。6カ月および9カ月間保存した配偶体の平均生残率はそれぞれ68.4%、40.0％に低下し、9カ月の保存配偶体のFv/Fmは保存前の約70%の値に、NPQは約50%の値に低下した。Fv/FmとNPQはマコンブ配偶体の生残率と有意な相関性が認められたことから、長期保存したマコンブ種苗等の生残性を評価する上でFv/FmとNPQが有効な指標となることが明らかになった。
  • 文部科学省：科学研究費補助金(基盤研究(C))
    研究期間 : 2013年 -2015年 
    代表者 : 水田 浩之
     
    コンブ類の傷害抵抗性を誘導する条件を探索し、その機構解明を試みた。その結果、マコンブ幼胞子体への赤色光照射により、他の光(青色光、緑色光及び白色光)では認められない体の硬化を導くことが明らかになった。そこでリグニン様物質を測定したところ、赤色光下の幼胞子体は他の光条件のものに比べ高い含有量を示していた。また、赤色光照射による活性酸素発生の誘導や、表皮細胞の細胞壁に高いペルオキシダーゼ活性とリグニン様物質の分布が観察された。以上のことから、赤色光照射は、ペルオキシダーゼと活性酸素によって触媒されるリグニン様物質の合成を促し、葉状部の硬化を導き、物理的な抵抗力を付加する可能性を示唆した。
  • 文部科学省：科学研究費補助金(基盤研究(C), 基盤研究(C))
    研究期間 : 2010年 -2012年 
    代表者 : 水田 浩之
     
    コンブ類の繁殖における静的防御機構(健全な藻体に存在する本来備えている抵抗機構)に関与する新たな化学成分の検索を目的とし、マコンブ胞子体の栄養成長期と生殖成長期(子嚢斑と呼ばれる生殖器官形成期)にある葉状部組織のケイ素含有量を測定すると共に組織化学的観察を行った。その結果、子嚢斑形成部位において隣接する未成熟部位に比べ高いケイ素含有量を示した。成熟部位においてケイ素は、子嚢斑を形成する側糸と呼ばれる遊走子(無性生殖細胞)嚢を保護する役割を担うと言われている部分とそれを保護するため側糸先端部に形成される粘液帽に分布していた。また、未成熟部位でもケイ素が含まれ、表皮細胞と皮層細胞の間の細胞間隙に分布し、葉状部の物理的強度の低いと考えられる縁辺部分や先端部分の比較的厚さの薄い部分で高い含有量を示す傾向が認められた。特に、傷害を受けたのち治癒した部分において高いケイ素の含有量を示し、傷害を覆うように分布することが観察された。これらのことから、ケイ素が胞子体が成長していく過程のみならず、コンブ類の胞子体の生殖器官の形成およびその保護に大きく関わり、繁殖の成功に大きく寄与していることが明らかになった。加えて、チガイソ科褐藻の胞子葉(めかぶと呼ばれる生殖器官)でも高いケイ素含有量を示す傾向が認められたことから、生殖器官の保護に寄与するケイ素の役割は、コンブ科褐藻だけでなくチガイソ科褐藻を含めたコンブ類に広く共通するものであると考察された。さらに、大型海藻類においてケイ素の機能や必須性は明らかにされていなかった元素であり、本研究成果は、海藻類の栄養要求における学術的にも貴重な基礎的知見である。
  • 文部科学省：科学研究費補助金(基盤研究(C))
    研究期間 : 2004年 -2006年 
    代表者 : 水田 浩之
     
    海藻類のカルス細胞の誘導及び増殖技術には、摘出組織からのカルスの量が少ないこと、カルスの増殖速度が極めて遅いこと、カルスの分化を制御できないなどの問題点がある。これらの問題点を解決し、より実用的な培養系を確立するためには、カルス誘導条件とその過程の把握が必要となるだけでなく、成長,成熟,脱分化,再分化等のメカニズムの解明を視野においた基礎的研究と技術開発が求められる。そこで、本研究では、カルス誘導の効率誘導と増殖促進条件を明らかにすると共に、そのメカニズムについても考察した。その結果、下記のことが明らかになった。1.カルス誘導の最適水温および塩分条件は、未切断の葉状体と類似の傾向を示した。すなわち、水温10℃で最も高い誘導率を示し、塩分が27.5psu以上の時に、高頻度でカルスが形成された。2.貧栄養滅菌海水中でのカルス誘導率は、富栄養海水中のそれに比べ低く、その後の成長が停止した。また、ビタミン類の添加によるカルス誘導率の促進効果は認められなかった。3.キレート剤であるEDTA, EGTA, NTAの添加は、カルス誘導をわずかに促進したか、左右しない程度であった。しかし、キレート剤と共に栄養補強剤を添加すると、カルスの誘導率は低下した。4.暗条件下でも糸状のカルスが誘導されるが、その後の成長は低下した。また、高光量で誘導されたカルスの成長はやがて止まり、脱色を招いた。このことは、独立栄養により成長可能であることを示すと共に,光量は誘導よりその後の成長を左右する大きな要因であると考えられた。赤色光の照射は、白色光や青色光に比べ、成熟を阻害すると共に赤色光は胞子体茎状部および付着器の伸長を促進した。また、赤色光はカルスの形成とその成長を促進した。これに対し、青色光は葉状体の成熟を促進した。5.カルス誘導の栄養要求において、植物成長調整物質が有効であることが明らかになった。コンブ類のカルス誘導には、オーキシンおよびサイトカイニンの同時添加が好ましいことが分かった。特に、オーキシンは細胞分裂と伸長を、サイトカイニンは白色化の抑制に効果的であると考えられた。カルスの誘導は、コンブ葉状体の部位によって大きく異なり、基部に近い部位から得た藻体片において高頻度でカルスの誘導が認められ,先端部ほどカルスの誘導率は低下した。これは、分裂活性に比例していると思われ、体内のオーキシンおよびサイトカイニン含有量の違いによるものと推察された。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2003年 -2005年 
    代表者 : 嵯峨 直恆, 安井 肇, 水田 浩之, 北出 幸広
     
    本研究により得られた新たな知見等は以下のとおりである。 1.単胞子未形成時よりも単胞子形成時に発現量が増加する遺伝子の探索について cDNAマクロアレイ法による1次スクリーニングと、RT-PCR法またはノーザン解析による2次スクリーニングを行った結果、代謝に関わる酵素をコードする8個の遺伝子のほか配偶体特異的な発現パタンを示す機能未知の遺伝子が見つかった。上記8遺伝子については、cDNA全長配列を決定し、DDBJへの登録手続きを行った(AB127044-AB127051)。 2.スサビノリ遺伝子の発現解析手法と内部基準の開発について (1)エロンゲーションファクター1α遺伝子のリボプローブを用いて、配偶体世代の発芽体におけるホールマウントin situハイブリダイゼーション法を開発した。 (2)差次的発現をする遺伝子の発現解析における新たな内部基準(アクチン関連タンパク質4ホモログ)を開発した。本遺伝子の演繹アミノ酸配列中には推定のbipartite型核局在シグナル(NLS)とアクチンモチーフが見つかった。本遺伝子の発現レベルは、生活環の4つの発生段階で有意に変化せず、従来型アクチンよりも低かった。 3.化学物質による単胞子形成誘導法について 10mMのアラントインを含む培地で栄養成長したスサビノリ配偶体を培養することにより発芽能力のある単胞子様細胞が得られることがわかった。また、この処理により本来単胞子を介した無性生殖をしない種(ウップルイノリ)でも同様の細胞が得られることがわかった。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2003年 -2005年 
    代表者 : 門谷 茂, 工藤 勲, 水田 浩之, 多田 邦尚, 柳 哲雄, 堤 裕昭
     
    本研究では、地球上で最も単位面積当たりの動物生産量が高い場であるとされながらも、研究上のさまざまな隘路により、これまで包括的な知見が極めて限られていた干潟域における基礎生産過程や、それに続く食物網のダイナミクスについて、詳細かつ長期の調査研究を基礎として、さまざまな素過程の定量化を進めるとともに、将来の環境管理に必要不可欠である干潟域の生態系モデルの構築を同時に実施する事を計画して実施した。我が国のように南北に細長く温度環境等が大きく異なる環境場に点在する干潟群の汎用的なモデル化を、1カ所の干潟での観測例のみで構築することは不可能である。そこで、我々の研究チームは、北海道から九州までの代表的な3カ所の干潟を選定し、それぞれの場所で同質・同種の観測・実験結果を得て、従来知見の乏しかった底生生物の親生物元素動態にはたす役割を定量化するとこで、我が国では初めてのケースとなる基礎生産から高次生産まで含めた包括的な生態系モデルを構築することを目的とした。高松の河口干潟において実施された研究により、底生珪藻の基礎生産量を正確に見積もることができた。また、そのレベルは、瀬戸内海の海水中の基礎生産量を超える値であることを明らかにした。さらに、底生動物と環境因子の関係について詳細に把握した。その結果、生物は環境因子により生物量やその組成に影響を与えられるが、逆に生物自自身が環境を作り替えていることも明らかにした。最終的に、干潟域での包括的な生態系モデルを作成することに成功した。
  • 文部科学省：科学研究費補助金(奨励研究(A))
    研究期間 : 1997年 -1998年 
    代表者 : 水田 浩之
     
    マコンブLaminaria japonica胞子体片を用いて培養条件下で成熟誘導を試みた。また、自然環境下での子嚢斑形成状況と比較検討した結果、以下のことが明らかになった。1. 胞子体片を用いてた培養で子嚢斑形成が可能となった。2. 子嚢斑形成は15℃で最も早く、かつ大きな子嚢斑を形成した。3. 子嚢斑面積は高光量ほど大きかったが、その形成時期は光量に左右されにくかった。4. 短日条件下での子嚢斑形成は、等日および長日条件下に比べ早かった。5. 貧栄養条件は胞子体片の子嚢斑形成を遅らせかつ、その面積を著しく制限した。6. 子嚢斑形成には、ある一定以上の栄養元素の蓄積が必要であることが示唆された。7. 胞子体基部に比べ先端部の胞子体片の方が子嚢斑形成が早く、また中帯部に比べ縁辺部の方が容易に子嚢斑を形成する傾向が見られた。8. 自然環境下での子嚢斑形成は縁辺部に先立ち中帯部から形成される場合が多かった。9. 視覚的な子嚢斑形成以前に既に胞子体片内では種々の変化生じており、その変化は光合成の低下、呼吸の増加、タンパク質合成に特徴づけられる。10. ホソメコンブ、ガゴメ、アナメ胞子体片でも子嚢斑を形成させることができた。以上の結果から、一年中を通して個体やその採取部位によらず胞子体片を培養することにより子嚢斑を形成させることが可能であることが示された。この胞子体片を用いたマコンブは他のコンブ属植物にも応用でき、採苗方法は時期に左右されずに付着生物等の影響の少ない種苗を提供し得る可能性を示すものである。

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